This invention relates to secondary containment systems for preventing the escape of materials that may leak from a primary containment system, and has particular reference to a secondary containment system for a primary pipe system of pipes joined together in various configurations by pipe joints having pipe sockets for receiving the ends of the pipes. The pipes are secured and sealed in the sockets in various ways that are intended to prevent leakage of fluid from the primary system.
Protection of the environment from polution by leakage from primary containment systems is a major problem today and is receiving increasing attention, from both industry and government. More and more attention and effort are being devoted to both clean-up of existing spills and prevention of further contamination by existing and new containment systems. The consequences of such spills have been very serious, and the expense of clean-up efforts can be enormous, making it both environmentaly and economically important to prevent leakage of hazardous materials, typically chemical and petroleum products but also including sewage.
Governmental regulations in the United States now require secondary containment on many new installations, such as chemical storage systems, and will require secondary containment on many pre-existing systems within a few years. Even now, there are existing primary pipe systems that are leaking, or susceptible to leaking, so as to require the installation of protective secondary containment systems. There is, therefore, a significant need for a practical and economical secondary containment system.
Several different approaches have been suggested for the secondary containment problem, one of the relatively recent approaches being described in U.S. Pat. No. 4,786,088. This patent discloses a double-containment thermoplastic pipe assembly comprising a containment pipe and carrier pipe joined by relatively complex restraint couplings and pipe joints, some of the latter being of a split configuration to be welded together around a primary pipe joint. Other secondary containment approaches are identified or discussed in the Background section of this patent, along with some generally related dual systems, connectors and the like.
Another example of a dual system is U.S. Pat. No. 4,374,596, which discloses an electrical duct connector with longitudinally divided pipe sections and pipe fittings that can be snapped together. U.S. Pat. No. 3,572,395 shows a generally similar split elbow joint. Other representative prior secondary containment pipe systems and elements are shown in U.S. Pat. Nos. 3,721,270, 3,802,456, 4,422,675 and 4,673,926, all concerned with the containment of leakage from primary pipes and joints. The '926 patent illustrates an important auxiliary feature of such systems, the provision of leak detection and signaling means in the secondary containment systems, so that corrective action can be taken to terminate leakage from the primary system into the secondary system.
Yet another approach, used by Harrington Industrial Plastics, Los Angeles, Calif. and elsewhere, has been the use of standard thermoplastic pipe and fittings, of a material such as polyvinylchloride ("PVC"), with oversize secondary containment pipes telescoped over the primary pipe and joined over the conventional primary pipe joints by oversize secondary containment fittings that have been cut, usually by sawing, into two pieces that can be reassembled, clamshell fashion, around the primary pipe joint. These fittings then are bonded together, as by hot-welding of the saw-cut edges, and are suitably sealed to the secondary pipes, usually with a sealing cement. Arcuate spacers with radially extending fingers have been provided in different sizes to maintain the two pipe systems in spaced coaxial relation.
Despite all of these prior efforts to provide effective, practical and reasonably priced secondary containment systems, there as yet is no system that is completely satisfactory. Many suffer from undue complexity and cost in manufacture, assembly, or installation, and most are not capable of being practically applied to an existing primary system, to provide effective secondary containment on a retrofit basis.